Separate the idea of clients and connections

We would like to be able to add other client types besides linaro images, such as ssh or qemu or fast models. To support doing that, it would be useful if the device config could specify the client type. We should also take this opportunity to clean up the existing client code a bit.

Related branches

Related bugs

Sprints

Whiteboard

Meta:
Headline: Client type is now a configuration option for devices in LAVA
Acceptance: Clients can be configured per device, and imply a separate connection
Roadmap id: LAVA2011-A15-FAST-MODEL-INTEGRATION

Work Items

Work items:
separate the idea of connections from clients: DONE
sanitize and merge the Android client into the regular Lava Client (perhaps this should get renamed to LinaroClient?): DONE
Add board configuration support for the client type: DONE